The precise regulation of salt and water excretion and reabsorption by the kidney is necessary for maintaining the composition and volume of body fluids. The failure to regulate salt and water transport by the kidney can be linked to a number of diseases. With the advent of several new techniques in electrophysiology, it is possible to understand more clearly the mechanisms involved in renal salt and water transport and the factors which control renal function. Furthermore, an evaluation of these regulatory factors will provide a better understanding of the pharmacological action of loop diuretics commonly used in the treatment of hypertension. The aims of this project are to study the mechanism of chloride transport across individual cell membranes of the proximal and the early distal tubule of two amphibian species, Necturus maculosus and Amphiuma means, and to identify how mechanisms located on separate cell membrane are regulated to maintain cell homeostasis and to coordinate transepithelial ion transport. Two possible factors, intracellular calcium and c-AMP, which have been implicated in the control of many transport systems, will be evaluated for a possible role in regulating chloride transport. In addition, the mechanisms and specific location of the effects of two diurectics, furosemide and amiloride will be evaluated. The experiments will include the simultaneous measurement of cell volume and intracellular ion activities using a combination of microelectrodes and video-optical techniques to monitor changes in intracellular ion content during several experimental maneuvers.